The present invention relates to IP telecommunications and more particularly to the use of IP technology for transmitting voice and other user traffic in a telecommunications system.
In conventional telecommunications networks, voice data and other user generated data is sent between telephone exchanges or xe2x80x9cswitchesxe2x80x9d using time division multiplexing over Synchronous Transfer Mode (STM) networks. In Europe, the E.1transmission protocol is used which divides time frames into slots such that corresponding slots in successive frames provide a 64 Kbits/second data channel. In the USA, a similar transmission protocol, referred to as T.1, is used.
A call connection is set up by reserving an end-to-end data channel between the originating exchange and the terminating exchange (possibly via one or more intermediate or xe2x80x9ctransitxe2x80x9d switches). The signalling necessary to set-up the connection, as well as to control and terminate the connection, uses the ISDN User Part (ISUP) signalling protocol which forms part of a Signalling System no.7 (SS7) signalling protocol stack. More particularly, a connection is reserved by propagating an ISUP Initial Address Message (LAM) from the originating exchange to the terminating exchange, the LAM containing an identification of the originating and terminating exchanges using so-called xe2x80x9cPoint Codesxe2x80x9d (PCs). For each inter-exchange link in the connection, the IAM carries forward an identification of the channel to be reserved for the connection. This identification is referred to as a Circuit Identification Code (CIC).
There currently exists a high level of interest in employing Internet Protocol (IP) technology in telecommunications networks both for the transmission of signalling traffic (e.g. ISUP messages) and user data. The advantages of using IP are an increase in network capacity due to replacing circuit switched channels with packet switched channels and potential cost savings due to the low cost of IP systems relative to conventional telecommunications systems.
In the event that two telephone exchanges are coupled via a conventional IP network for the transmission of user data, the IP network will route the data in the form of a sequence of IP datagrams between successive IP routers. The routers rely on so-called xe2x80x9cbest effortsxe2x80x9d to relay datagrams which means that datagrams are forwarded to the next router in the chain only if capacity on the interconnecting link is available. If sufficient capacity does not exist, then the packet is discarded, and a message returned to the originating switch advising that switch to resend the packet. It will be appreciated that this best efforts transmission service is not well suited to voice telephony or other forms of data transmission where real time or close to real time transmission is required.
ISUP comes in a number of national variants characterising different regulatory environments. Even within a given country, different operators may use different ISUP protocols which in turn differ from the inter-national ISUP protocol(s). In conventional telecommunication networks, gateway exchanges are able to convert between the ISUP variant of its home network and the variants of the xe2x80x9cforeignxe2x80x9d networks to which it is connected. Thus only a limited number of conversions are required at any one gateway exchange.
Consider now the situation which arises if two PSTNs are coupled via a Voice over IP (VoIP) network. ISUP signalling messages must be transferred between the two gateway nodes of the PSTNs and this may be done over that same IP network or over some other network. If the VoIP network replaces for example an International trunk then every gateway node connecting to the VoIP network must be able to convert ISUP messages of its home network into every one of the other national ISUP variants (which exist for foreign networks also coupled to the same VoIP network) and vice versa. This problem arises because a sequence of ISUP conversions is no longer carried out as the ISUP messages are passed along a chain of gateway exchanges.
Assuming that there are 60 national ISUP variants, then each gateway exchange must be capable of handling 60xc3x9760 or 3600 ISUP conversions. The provision of this number of conversions is difficult or even impossible to provide in practice.
It is an object of the present invention to overcome or at least mitigate the above noted disadvantage. It is a second object of the present invention to enable the transmission of user data using IP such that the delivery of the data is guaranteed. It is a third object of the present invention to reduce the number of ISUP conversions which must be provided for in a given gateway switch.
These and other objects are achieved at least in part by co-locating certain IP nodes of the IP network with gateway signalling points of the signalling network.
According to a first aspect of the present invention there is provided a telecommunications system comprising a signalling network and a Voice over IP (VoIP) network, the signalling network comprising gateway signalling points for converting signalling messages between at least two different signalling protocols and the IP network comprising IP nodes for routing IP datagrams, at least certain of the IP nodes being co-located with respective gateway signalling points, the co-located signalling points being arranged in use to pass routing information to the respective IP nodes to enable those nodes to prioritise and route incoming IP datagrams.
According to a second aspect of the present invention there is provided a method of setting up a call connection over a sequence of nodes of an Internet Protocol (IP) network, where each of said nodes is co-located with a signalling point of an SS7 signalling network, and with each IP node being identified by an IP address and each SS7 signalling point being identified by a Point Code (PC), the method comprising:
allocating to each link of the connection, at the SS7 signalling point level, a Circuit Identification Code;
notifying each IP node of the CIC of the or each link to a neighbouring IP node, and of the PC of the or each neighbouring signalling point;
at each IP node, translating the received PC and CIC combination(s) into an IP address and port number for the or each neighbouring IP node; and
defining at each IP node a priority delivery service for datagrams received from the or each IP address and port number combination.
It will be appreciated that once the connection is set-up between the sequence of IP nodes, an IP datagram received at an IP node can be analysed on the basis of either the IP address and port number from which it originated or the IP address and port number to which it is delivered to determine whether or not delivery of the datagram to the next IP node in the sequence is a priority action. It will also be appreciated that the IP addresses and port numbers derived for neighbouring nodes and channels may be used to route outgoing datagrams. For example, for a given connection, the IP node may contain mapped pairs of IP addresses and port numbers, e.g. {IP1,PNo1),(IP2,PNo2)}, such that a datagram received from one of the pair (IP2,PNo2) is routed as a priority to the other of the pair (IP2,PNo2).
The method of the present invention may be used to provide a call connection between two Plain Old Telephone Systems (POTS), where each of the POTS comprises a gateway node which converts user data between an IP format and a POTS format. Alternatively, the invention may be used to connect two Internet enabled terminals via respective access networks, where user data is transferred across the access networks in an IP format. The local exchange of such an IP enabled terminal may, for example, maintain a register mapping terminal (or subscriber) telephone numbers to IP addresses.
Whilst one suitable use for the method of the present invention is the setting up of Voice over IP calls, it will be appreciated that the invention also applies to setting up connections for the transfer of other forms of user data, e.g. facsimile, video conferencing.
According to a third aspect of the present invention there is provided a method of relaying datagrams at a node of an IP network which node is co-located with a signalling point of an SS7 network, wherein the IP node retains a set of IP address and port number combinations derived on the basis of PC and Circuit Identification Code (CIC) combinations passed to it by the co-located signalling point and identifying priority datagram transmissions, the method comprising:
receiving an IP datagram at said IP node;
comparing the originating IP address and port number combination of the received datagram with said set of IP address and port number combinations; and
in the event that said originating IP address and port number combination are contained in the list, relaying the datagram to a subsequent IP node as a priority and, in the event that said originating IP address and port number combination are not contained in the list, using only best effort to relay the datagram to a subsequent IP node.
According to a fourth aspect of the present invention there is provided a node of an IP network, the node being arranged to be coupled to neighbouring nodes for the purpose of setting up a call connection, and each of the nodes being arranged to be co-located with respective signalling points of an SS7 signalling network, the node comprising:
first processing means for receiving Point Code (PC) and Circuit Identification Code (CIC) combinations passed to the node by the co-located signalling point, which combinations identify priority datagram transmissions, and for deriving IP address and port number combinations on the basis of said PC and CIC combinations;
a memory for storing said set of IP address and port number combinations;
receiving means for receiving an IP datagram sent from one of said neighbouring nodes; and
second processing means for comparing the originating IP address and port number combination of the received datagram with said stored set of IP address and port number combinations and, in the event that said originating IP address and port number combination are contained in the list, for relaying the datagram to a subsequent IP node as a priority and, in the event that said originating IP address and port number combination are not contained in the list, for using only best effort to relay the datagram to a subsequent IP node.